For the realization of the therapeutic and research potential of human embryonic stem cells (hESCs), methods must be developed for their long term culture in an undifferentiated and karyotypically normal state. BresaGen Inc. has three of the NIH registered hESC lines actively growing, (BG01, BG02, BG03). The Company has partially characterized two of these lines (BG01, BG02) and made them available to the research community. All three hESC lines will be characterized and cell stocks generated under 'good laboratory practice' will be distributed. hESCs will be made available to researchers in three formats: as manually passaged cells, as trypsin passaged cells, and as feeder free subclones. The impact of different culture methods on the stability of hESCs will be assessed with particular attention focused on the karyotype, pluripotent state and differentiation potential of the cells. Cell surface carbohydrate epitopes and protein antigens will be more completely characterized for each hESC line, generating tools which may be useful in isolating or characterizing hESCs. There is an urgent need to compare different hESC lines, either cultured in different laboratories or under different conditions. A microarray system for the assessment of hESC cultures will be developed and made available to the research community. These proposals are designed to meet important needs within the hESC community and facilitate research progress toward clinical applications.